This application claims priority to Great Britain application number 9619117.6, filed Sep. 12, 1996.
1. Field of the Invention
The present invention relates to digital image processing and is of particular applicability to the processing, for example colour correction, of images during transfer from cinematographic film to videotape by means of a telecine machine.
2. Description of Related Art
Telecine machines scan cinematographic film, and derive electrical signals therefrom corresponding to the images on the film for recording onto videotape or broadcasting as television pictures. One such example of this is the xe2x80x98URSAxe2x80x99 telecine, manufactured by Rank Cintel Ltd. in Ware, England.
It is known to have a so-called grading mode for these telecines, wherein scenes are studied, and a colour correction data set is visually determined for a particular scene. The process of building up a series of colour correction values for a number of scenes, which is then used in a real time xe2x80x98transferxe2x80x99 mode is taught in U.S. Pat. No. 4,096,523. A telecine controller and programmer which may be used in such a system is the xe2x80x98POGLExe2x80x99 from Pandora International Ltd.
Although telecine systems as described above often contain the facilities to alter the reproduced colour of the pictures produced on videotape or television broadcast, these facilities are usually limited in their selectivity. The Rank Cintel URSA, for example, has the ability to correct either in a primary or secondary mode. In the primary mode, the overall redness, for example, of the entire image may be increased. In this case, all colours and greys that contain red will be reproduced with a higher red content. In the secondary mode, the system initially distinguishes between greys and colours; greys are left unchanged, whilst colours are arranged into one of six types, each of which can be modified independently.
If it is required to process colours more selectively (for example to modify light reds without altering dark reds) it is necessary to use a more sophisticated colour corrector. One such system is the xe2x80x98Digital Colour Processorxe2x80x99 (DCP) manufactured by Pandora International Ltd., of Northfleet, Kent. Such a system is described in UK patent application No. 2278514 and others.
International patent application WO 95/12289 describes a method of colour correcting a single object in an image. According to this document, an object is selected in a first frame by an operator and the position, shape and an appearance attribute, such as colour or texture, of the object are stored. A modification to the appearance attributes of the object is also stored. The position, shape and an appearance attribute of the object in a subsequent, second frame are also stored. The modification of the appearance attributes of the object in the frames between the first and second frames is effected by interpolating between the two positions and shapes to calculate an expected position and approximate shape of the object in the intermediate frames. The pixels within the approximate shape at the expected position and having the selected appearance attribute of the object are then modified in each of the intermediate frames.